Two-part epoxy adhesives with improved flexibility and process for making and using same

ABSTRACT

A two-part epoxy adhesive having a resin component containing a mixture of an epoxy resin and an internally flexibilized epoxy resin and a hardener component containing a mixture of a flexibilizer and an unmodified or modified aliphatic amine or combinations thereof. The resin component and hardener component are mixed and applied to substrates, or applied to substrates and mixed, an then allowed to cure yielding a cured epoxy resin having a tensile elongation at room temperature of greater than 30%. The initial curing time is less than 3 hours.

BACKGROUND OF THE INVENTION

[0001] This invention relates to two-part epoxy adhesives which have improved flexibility and a process for making and using them. More particularly, this invention relates to an improved epoxy adhesive which has good adhesions to various substrates, especially where a high level of elongation is needed due to thermal expansion and contraction of the substrates or where the substrates are exposed to thermal shock. It can also be used at low operating temperatures.

[0002] Polymeric compositions based on the commercially available Bisphenol A based epoxy resins cured by one or more of the active hydrogen compounds such as polyamines, polyacids, polyphenols, and the like exhibit good adhesion properties towards various substrates including metal and plastics, but most of these adhesives are rigid, stiff and brittle polymers. There is also a problem of shrinkage occurring in the epoxide adhesive during the curing, thus building undesired stress in the substrates as well as the adhesive at the glue line. Accordingly, it has been suggested that flexibilizers such as butadiene rubbers, urethane elastomers, and the like be added to the epoxy resins.

[0003] Past attempts to modify epoxies involved reacting them with copolymers of butadiene, acrylonitrile or other “rubber”-based compositions. See Journal of Applied Polymer Science, Vol. 26, pp. 907-919 (1981). By reacting an epoxy with those compounds and then processing the modified composition to induce in situ phase separation, “rubber rich” domains within the epoxy composition are created. Those domains improve the toughness of the cured epoxy matrix once it is formed. However, while such modified epoxy compositions are tougher and less brittle at room temperature, improvements at lower temperatures prove to be, at best, marginal. Further, using the above-mentioned rubber-based material incurs processing problems due to an increase in viscosity of the adhesive mixture.

[0004] Accordingly, various epoxy adhesive formulations have been proposed to address these problems. See, for example U.S. Pat. No. 4,728,384; 5,098,505; 5,218,063; 5,367,006 and 5,679,730. More recently, there has been introduced Mr. Sticky's Underwater Glue. According to the website at underwaterglue.com, this is an improved two-part epoxy glue having a flexibility (elongation) of 30%, very good shock dampening, and flexible bonds. It has a mixture working life of 30-60 minutes and an initial curing time of 3-4 hours. The complete curing time is 24 hours.

[0005] Still, there is a need for an even more improved two-part epoxy adhesive.

SUMMARY OF THE INVENTION

[0006] That need is met by the present invention which provides a two-part epoxy adhesive with improved flexibility and provides a process for adhering at least two substrate surfaces to each other with that adhesive.

[0007] The two-part epoxy adhesive has a resin component made up of a mixture of an epoxy resin such as a standard, undiluted, liquid Bishpenol-A resin, and an internally flexibilized epoxy resin which is also preferably a Bisphenol A type resin. The resin component may also contain a plasticizer/accelerator, such as a phenol base plasticizer/accelerator, a coupling agent such as an epoxide functional silane base coupling agent, fillers, such as limestone filler and titanium dioxide white pigment, and a thixotropic agent.

[0008] The percentages by weight in the preferred embodiment of the resin component are:

[0009] 30-75% epoxy resin,

[0010] 5-40% plasticizer/accelerator,

[0011] 0.1-1% coupling agent,

[0012] 11-45% filler, and

[0013] 1-8% thixotropic agent.

[0014] The two-part epoxy adhesive has a hardener component made up of a mixture of a flexibilizer, such as an amine terminated butadiene acrylonitrile adduct, and an unmodified aliphatic amine, such as an unmodified glycol ether base aliphatic amine or a modified aliphatic amine such as an Aminoethyl-piperozine (AEP) base modified amine, or combinations thereof. The hardener component may also contain an accelerator, which is preferably a tertiary amine accelerator, as well as a thixotropic agent.

[0015] The percentages by weight in the preferred embodiment of the hardener component are:

[0016] 20-80% flexibilizer,

[0017] 5-30% unmodified aliphatic amine,

[0018] 1-10% accelerator,

[0019] 10-50% modified aliphatic amine, and

[0020] 1-8% thixotropic agent.

[0021] The most preferred two-part epoxy adhesive has:

[0022] a) a resin component comprising a mixture of:

[0023] 40-45% Bisphenol A epoxy resin,

[0024] 8-15% internally flexibilized Bisphenol A type epoxy resin,

[0025] 10-20% phenol base plasticizer/accelerator,

[0026] 0.3-0.6% epoxide functional silane base coupling agent,

[0027] 15-25% limestone filler,

[0028] 0.5-2% white pigrnent and

[0029] 4-6% thixotropic agent, and

[0030] b) a hardener component comprising a mixture of:

[0031] 40-45% amine terminated butadiene acrylonitrile adduct,

[0032] 7-15% unmodified glycol ether base aliphatic amine,

[0033] 5-8% tertiary amine accelerator,

[0034] 25-40% AEP base modified amine, and

[0035] 1-8% thixotropic agent.

[0036] After the resin component and hardener component are mixed and reacted the cured epoxy adhesive has a tensile elongation at room temperature of greater than 30%, and the most preferred embodiment thereof has a tensile elongation at room temperature of greater than 120%.

[0037] In addition, the reactive mixture of resin component and hardener component has an initial cure time of less than 3 hours, and the most preferred embodiment thereof has an internal cure time of about 1.5-2 hours. The complete cure takes place in approximately 24 hours.

[0038] The epoxy adhesive of the present invention has good adhesion to various substrates including concrete, metals, plastics, and wood and is especially useful in applications where a high level of elongation (for example, when bonding to flexible PVC) is needed due to thermal expansion and contraction of the substrates (for example when bonding metal to plastic) or where the substrates are exposed to thermal shock. It is also useful in applications having low operating temperatures. While the preferred application temperature range is 40-100° F., it may be used at temperatures of up to about 180-200° F. and down to below zero to adhere at least two substrate surfaces to each other by intercalating between those surfaces an adhesive, formed from the reactive mixture of the resin component and the hardener component disclosed above, by applying these components in equal amounts (parts by volume) from a double-barreled cartridge, mixing well until the mixture is relatively homogeneous and applied relatively evenly to the substrates, and then allowing the adhesive to cure.

DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention provides an improved two-part epoxy adhesive having a resin component and a hardener component which can be dispensed from a double-barreled cartridge in equal parts by volume concurrently and then mixed until relatively homogeneous. As is known, dispensing and mixing may be prior to application of the relatively homogeneous mixture to one or more of the substrates, or it may take place on one or more of the substrates. Likewise, a double-barreled cartridge need not be used; the resin component and hardener component can be dispensed from separate containers and, then mixed. In any event, the reactive mixture of components is applied relatively evenly between substrates which are joined, and the adhesive is allowed to cure.

[0040] The initial cure takes place in less than 3 hours, and, with the two-part epoxy adhesive of the preferred embodiment, it has been found that generally the initial curing time is about 1.5 to 2.0 hours. Complete cure then takes place in about 24 hours.

[0041] After cure, the epoxy adhesive of the present invention has a tensile elongation at room temperature of greater than 30%, and with the two-part epoxy adhesive of the preferred embodiment it can exceed 120%. Elongation is important when bonding flexible materials like flexible polyvinyl chloride (PVC) or acrylonitrile-butadiene-styrene (ABS) and in those applications where there is a large amount of displacement between substrates or where the degree of thermal expansion and contraction is of concern.

[0042] The improved flexibility of the two-part epoxy resin of the present invention is achieved by using a resin component and a hardener component having a unique combination of ingredients. The resin component is a mixture of epoxy resin, which may be a standard, undiluted, liquid Bisphenol A resin such as EPON 828 from Shell Oil Company, Houston, Tex., and an internally flexibilized Bisphenol A type epoxy resin such as Araldite PY 322 available from Ciba Specialty Chemicals, Tarrytown, N.Y. The internally flexibilized epoxy resins have flexible segments in their backbone. Therefore when they react and become a part of the adhesive network, they provide flexibility into the rigid polymer via their soft/flexible segments. While Bisphenol A type resins are preferred, Bispehnol-F type resins or mixtures of the two can be used as either the core epoxy resin, or the internally flexibilized epoxy resin, or both.

[0043] The resin component may also contain a plasticizer/accelerator which may be a phenol base plasticizer/accelerator such as Nonylphenol from GE Specialty Chemicals, Morgantown, W. Va. Other plasticizers/accelerators may be used but Nonylphenol is preferred since it has minimal effect on physical properties and is a mild accelerator.

[0044] A small amount of coupling agent is also preferably added to the resin component. Preferred is an epoxide functional silane base coupling agent such as Silane Z-6040 from Dow Corning Corporation, Midland, Mich. That type of coupling agent, has dual reactivity, meaning that silanes, as is known, possess both organic and inorganic functionality that allow them to react with organic polymers and inorganic surfaces. An amino silane or other types of coupling agents could be used to get the same effect.

[0045] Any number of types of fillers can be added to the resin component. Preferred are limestone filler such as Marble White 325 from Filler Products Inc. and Titanium Dioxide R-900 white pigment from DuPont de Nemours, Wilmington, Del. Other white fillers and white pigments may be used for a white or off white colored resin component. If another color is desired, then fillers and pigments of the desired color would be used.

[0046] Finally, the resin component can contain a thixotropic agent such as Cab-o-Sil 720 from Cabot Corporation, Boston, Mass. There are numerous other thixotropic agents that could be used along with the fillers to obtain a resin component having the desired viscosity, i.e. one which permits dispensing as discussed above.

[0047] In preparation of the resin component, the core epoxy resin (EPON 828), the reactive flexibilizer (Araldite PY 322), the plasticizer/accelerator (Nonylphenol), and the coupling agent (Silane Z-6040) are mixed until the mixture is relatively homogenous, and then the fillers (Marble White 325 and Titanium Dioxide R-900) are added and mixed. As the last step, the thixotropic agent (Cab-o-Sil 720) is added and mixed until it is dispersed therein.

[0048] The preferred weight percentage range of the ingredients in the resin component and the most preferred range are as follows: RESIN COMPONENT Preferred Most Preferred Epoxy Resin 30-75 40-45 Internally Flexibilized Resin  5-40  8-15 Plasticizer/Accelerator  5-40 10-20 Coupling Agent 0.1-1   0.3-0.6 Limestone Filler 10-40 15-25 White Pigment 1-5 0.5-2   Thixotropic Agent 1-8 4-6

[0049] The hardener component contains a mixture of a flexibilizer, which may be an amine terminated butadiene acrylonitrile adduct, such as Hycor ATBN 1300×16 from B.F. Goodrich, Akron, Ohio, and an unmodified aliphatic amine, such as an unmodified glycol ether base aliphatic amine (i.e. Ancamine 1922A from Air Products, Pittsburgh, Pa.), or a modified base aliphatic amine such as an Aminoethyl-piperozine (AEP) base modified (Ancamine 1767, also from Air Products), or preferably a combination of the two. The flexibilizer does not have to be an amine terminated butadient acrylonitrile (ATBN) but it should be similar in mixture. For example, a carboxyl terminated butadiene acrylonitride (CTBN) can be used. Likewise, unmodified aliphatic amines other than glycol ether based ones can be used as long as they contribute to the toughness, resiliency and shock resistance of the cured adhesive and modified aliphatic amines other than AEP based ones can be used as long as they contribute to the toughness and speed up the cure, as do the AEP based ones.

[0050] The hardener component may also contain an accelerator, which may be a tertiary amine accelerator, such as Ancamine K-54 also from Air Products and a thixotropic agent, which can be the same as the one used in the resin component such as Cab-o-Sil 720 from Cabot. As was the case with the resin component, any thixotropic agent in an amount sufficient to give the desired viscosity may be used.

[0051] In preparation of the hardener component, all of the liquids, i.e., everything except the thixotropic agent, are blended and then the thixotropic agent is added and mixed until well dispersed therein.

[0052] The preferred weight percentage range of the ingredients in the hardener component and the most preferred range are as follows: Hardener: Component Preferred % Most Preferred % Flexibilizer 20-80 40-45 Unmodified Aliphatic Amine  5-30  7-15 Modified Aliphatic Amine 10-50 25-40 Accelerator  1-10 5-8 Thixotropic Agent 1-8 5-8

[0053] While two-part epoxy adhesives of the present invention are preferably used at 40-100° F. they may be at temperatures up to about 180-200° F., and are particularly useful at low temperatures down below about 0° F. They may be used for indoor or outdoor repair situations or in manufacturing OEM products where strong, flexible, but relatively permanent bonds are desired. They have good adhesion to various substrates including concrete, metals, such as steel, aluminum, brass, etc, plastics, such as ABS, PVC, flexible PVC, fiberglass, acrylics, polyurethanes, etc., and wood.

EXAMPLE

[0054] The resin component and hardener component were prepared by mixing the following ingredients as described above to prepare the two-part epoxy adhesive of the present invention: Parts by Tradename Ingredient Weight RESIN Epon 828 Bisphenol A Epoxy Resin 49.5 Araldite PY322 Internally Flexibilized 10.0 Bisphenol A Epoxy Resin Nonylphenol Plasticizer/Accelerator 16.5 Silene Z-6040 Coupling Agent 0.5 Marble White 325 Limestone Filler 17.0 Titanium Dioxide R-900 White Pigment 1.0 Cab-o-Sil 720 Thixotrophic Agent 5.5 HARDENER Hycar ATBN 1300x-16 Flexibilizer 41.7 Ancamine 1922A Unmodified Aliphatic Amine 10.6 Ancamine 1767 Modified Aliphatic Amine 35.0 Ancamine K-54 Accelerator 6.7 Cab-o-Sil 720 Thixotrophic Agent 6.0

[0055] The properties of the two-part epoxy adhesive were then compared to Mr. Sticky's Underwater Glue with the following results: Mr Sticky's Underwater Underwater Present Mr Sticky's Glue (data Glue (tested Invention Properties reported) data) (tested data) Color Off-White Off-White Off-White Viscosity @ 20° C. Resin 35,000 Hardener 200,000 36,000 Mixed Viscosity 35,000 Density (gr./cc) Resin 1.25 1.25 Hardener 0.94 0.97 Mixing Ratio by weight 4:3 1.2:1 by volume 1 to 1 1 to 1 Working Life 30-60 minutes 25-30 minutes Gell Time (25 gram) 3-4 hours 1.5-2 hours Full Cure 24 hours 24 hours Application Temperature 40°-100° F. 40°-100° F. TYPICAL PROPERTIES OF CURED PRODUCT Tensile elongation 30% 125% Tensile Modulus 76,000 psi Tensile Strength 2,000 psi 1,540 psi Flexural Modulus 82,000 psi LAP SHEAR TESTING CRS/CRS @ .010″ 1,800 psi 1,600 psi 1,600 psi RIGID PVC/PVC 1,300 psi 500 psi 1,100 psi ABRAIDED RIGID PVC/PVC 1,800 psi 850 psi 1,140 psi ABS/AB 400 psi 400 psi 800 psi ABRAIDED ABS/ABS 600 psi 710 psi 875 psi 180° T-PEEL TESTING RIGID PVC/FLEXIBLE PVC 12.6 pli 10.4 pli 10.5 pli ABRAIDED RIGID PVC/ FLEXIBLE PVC 25.4 pli 6 pli 10.1 pli ABS/FLEXIBLE/PVC 13.0 pli 3 pli 10 pli ABRAIDED ABS/FLEXIBLE/ N/A 11.1 pli 13.4 pli PVC 

What is claimed is:
 1. A two-part epoxy adhesive comprising: a) a resin component comprising a mixture of epoxy resin and an internally flexibilized epoxy resin, and b) a hardener component comprising a mixture of a flexibilizer and an unmodified or modified aliphatic amine or combinations thereof, wherein after said resin component and said hardener component are mixed and reacted the cured epoxy adhesive has a tensile elongation at room temperature of greater than 30%.
 2. The two-part epoxy adhesive of claim 1 wherein the epoxy adhesive has an initial curing time of less than 3 hours.
 3. The two-part epoxy adhesive of claim 1 wherein said resin-component further includes a plasticizer/accelerator, a coupling agent, fillers, and a thixotropic agent.
 4. The two-part epoxy adhesive of claim 1 wherein said hardener component further includes an accelerator and a thixotropic agent.
 5. The two-part epoxy adhesive of claim 1 wherein said resin component comprises by weight: 30-75% epoxy resin, 5-40% internally flexibilized epoxy resin, 5-40% plasticizer/accelerator, 0.1-1% coupling agent, 11-45% filler, and 1-8% thixotrophic agent.
 6. The two-part epoxy adhesive of claim 5 wherein said epoxy resin is a Bisphenol A epoxy resin, said internally flexibilized epoxy resin is an internally flexibilized Bisphenol A type epoxy resin, said plasticizer/accelerator is a phenol based plasticizer/accelerator, said coupling agent is an epoxide functional silane base coupling agent and said filler is a mixture of limestone filler and white pigment.
 7. The two-part epoxy adhesive of claim 6 wherein said hardener component comprises by weight: 20-80% flexibilizer 5-30% unmodified aliphatic amine, 1-10% accelerator 10-50% modified aliphatic amine, and 1-8% thixotropic agent.
 8. The two-part epoxy adhesive of claim 7 wherein said flexibilizer is an amine terminated butadiene acrylonitrile adduct, said unmodified aliphatic amine is an unmodified glycol ether base aliphatic amine, said accelerator is a tertiary amine accelerator, and said modified aliphatic amine is an AEP base modified amine.
 9. A two-part epoxy adhesive comprising: a) a resin component comprising a mixture of epoxy resin and an internally flexibilized epoxy resin, and b) a hardener component comprising a mixture of flexibilizer and an unmodified or modified aliphatic amine or combinations thereof, wherein the reactive mixture of said resin component and said hardener component has an initial curing time of about 1.5-2 hours and after curing the epoxy adhesive has a tensile elongation at room temperature of greater than 120%.
 10. The two-part epoxy adhesive of claim 9 comprising: a) a resin component comprising a mixture of: 40-45% Bisphenol A epoxy resin, 8-15% internally flexibilized Bisphenol A type epoxy resin, 10-20% phenol base plasticizer/accelerator, 0.3-0.6% epoxide functional silane base coupling agent, 15-25% limestone filler, 0.5-2% white pigment and 4-6% thixotrophic agent, and b) a hardener component comprising a mixture of: 40-45% amine terminated butadiene acrylonitrile adduct, 7-15% unmodified glycol ether base aliphatic amine 5-8% tertiary amine accelerator, 25-40% AEP base modified amine, and 1-8% thixotrophic agent.
 11. The process of adhering at least two substrate surfaces to each other comprising the acts of: intercalating between said surfaces an adhesive comprising a reactive mixture of: a. a resin component comprising a mixture of epoxy resin and internally flexible epoxy resin, and b. a hardener component comprising a mixture of a flexibilizer and an unmodified or modified aliphatic amine or combinations thereof, and allowing said adhesive to cure, whereby said cured adhesive has a tensile elongation at room temperature of greater than 30%.
 12. The process of claim 11 wherein in said act of curing it takes less than 3 hours for initial curing.
 13. The process of claim 12 wherein said act of intercalating includes dispensing the resin component and hardener component in equal parts by volume and mixing until the mixture is relatively homogeneous and is applied relatively evenly to the substrates.
 14. The process of claim 11 wherein said resin-component further includes a plasticizer/accelerator, a coupling agent, fillers, and a thixotropic agent.
 15. The process of claim 11 wherein said hardener component further includes an accelerator and a thixotropic agent.
 16. The process of claim 11 wherein said resin component comprises by weight: 30-75% epoxy resin, 5-40% internally flexibilized epoxy resin, 5-40% plasticizer/accelerator, 0.1-1% coupling agent, 11-45% filler, and 1-8% thixotrophic agent.
 17. The process of claim 16 wherein said epoxy resin is a Bisphenol A epoxy resin, said internally flexibilized epoxy resin is an internally flexibilized Bisphenol A type epoxy resin, said plasticizer/accelerator is a phenol based plasticizer/accelerator, said coupling agent is an epoxide functional silane base coupling agent and said filler is a mixture of limestone filler and white pigment.
 18. The process of claim 17 wherein said hardener component comprises by weight: 20-80% flexibilizer 5-30% unmodified aliphatic amine, 1-10% accelerator 10-50% modified aliphatic amine, and 1-8% thixotropic agent.
 19. The process of claim 18 wherein said flexibilizer is an amine terminated butadiene acrylonitrile adduct, said unmodified aliphatic amine is an unmodified glycol ether base aliphatic amine, said accelerator is a tertiary amine accelerator, and said modified aliphatic amine is an AEP base modified amine.
 20. The process of claim 11 wherein: a) said resin component comprises a mixture of: 40-45% Bisphenol A epoxy resin, 8-15% internally flexibilized Bisphenol A type epoxy resin, 10-20% phenol base plasticizer/accelerator, 0.3-0.6% epoxide functional silane base coupling agent, 15-25% limestone filler, 0.5-2% white pigment and 4-6% thixotrophic agent, and b) said hardener component comprises a mixture of: 40-45% amine terminated butadiene acrylonitrile adduct, 7-15% unmodified glycol ether base aliphatic amine, 5-8% tertiary amine accelerator, 25-40% AEP base modified amine, and 1-8% thixotrophic agent.
 21. A process for making a two-part epoxy adhesive comprising: preparing a resin component by mixing an epoxy resin, an internally flexibilized epoxy resin, a plasticizer/accelerator, a coupling agent, fillers, and a thixotropic agent, and preparing a hardener component comprising a mixture of a flexibilizer, an unmodified or modified aliphatic amine or combinations thereof, an accelerator a thixotropic agent. 